Steering damper device

ABSTRACT

A steering damper device having a cylindrical damper disposed between a steering side member and a vehicle body side member, wherein said cylindrical damper includes a damper casing and a damper rod which is slidably displaced in the damper casing. The amount of slidable displacement of the damper rod with respect to a steering angle of the handlebar is small when the steering angle of the handlebar is near 0° and the amount of slidable displacement is larger as the steering angle is progressively changed from 0°. The damping coefficient of the cylindrical damper is large when the steering angle of the handlebar is near 0° and the damping coefficient is smaller when the steering angle is progressively changed from 0°.

FIELD OF INVENTION

The present invention relates generally to a steering damper device usedfor small-sized vehicles such as motorcycles.

BACKGROUND OF THE INVENTION

In general, motorcycles are steered by operating a handlebar so as toturn a front fork supporting a front wheel around a steering stem. Thesteering stem is rotatably inserted into a head pipe located at thefront end of a body frame. Such motorcycles are sometimes equipped witha steering damper device between a steering side member which is turnedby operating the handlebar and a body side member which is not turned byoperating the handlebar. In this case, the steering damper devicerequires at least the following conditions: damping moment is scarcelygenerated during normal traveling in which the steering angle of ahandlebar is small and its angular speed is low; high-damping moment isgenerated in the range where the steering angle of the handlebar islarge and the angular speed is high; and the damping moment is scarcelygenerated while the handlebar which has been turned is returned.

The present inventors have proposed a steering damper device that canmeet such requirements using a cylindrical damper which is simple inconfiguration and low in cost (Japanese Patent Application No.2003-301072). This steering damper device is configured such that thedamper is composed of a damper casing and a damper rod, one of them isrotatably connected to a vehicle body side member such as a head pipe orthe like, and the other is rotatably connected to a steering side membersuch as a fork bridge or the like. The damper is disposed so as to bemost contracted or extended when the handlebar is in the neutralposition, that is, when the steering angle of the handlebar is 0°.

With such a steering damper device, when the handlebar is turned to theright or left, the damper rod of the damper is slidably displaced in thedamper casing in the same direction, which provides symmetricaldamper-characteristics. When the handlebar is returned, the damper rodis slidably displaced in the opposite direction; therefore, a dampingforce can be allowed to be scarcely generated at that time. In addition,the amount of slidable displacement of the damper rod relative to thesteering angle of the handlebar is small when the steering angle is inthe vicinity of 0°; it is greater as the steering angle is larger than0°. Likewise, the damping force applied to the steering side member fromthe damper is small when the steering angle of the handlebar is near 0°;it is greater as the steering angle is progressively changed from 0°.Thus, the damping force is scarcely generated during normal traveling inwhich the steering angle of the handlebar is small and the angular speedis low, and high-damping moment is generated in the range where thesteering angle of the handlebar is large and the angular speed is high.

SUMMARY OF THE INVENTION

Incidentally, the steering damper device with the cylindrical damperdisposed in the way described above will have, in view of dynamics ofmechanism, characteristics in which the damping moment is increased asthe steering angle of the handlebar is increased. While suchcharacteristics are basically desirable for the steering damper device,the rider may feel hard steering when a large steering angle is requiredduring low speed traveling.

The present invention has been made in view of the foregoing and it isan object of the present invention to provide a steering damper devicecapable of assisting in operating a handlebar relatively nimbly even inthe range of large steering angles of the handlebar.

In order to achieve the above object, a first embodiment of the presentinvention provides a steering damper device having a cylindrical damperwhich is provided between a steering side member turned around asteering stem by operating a handlebar and a vehicle body side membernot turned by operating the handlebar. The cylindrical damper includes adamper casing and a damper rod which is slidably displaced in the dampercasing. As shown, for example, the steering damper device ischaracterized in that an amount of slidable displacement of the damperrod with respect to a steering angle of the handlebar is small when thesteering angle of the handlebar is in the vicinity of 0° and the amountof slidable displacement is larger as the steering angle isprogressively changed from 0°; and that a damping coefficient of thecylindrical damper is large when the steering angle of the handlebar isin the vicinity of 0° and the damping coefficient is smaller when thesteering angle is progressively changed from 0°.

Therefore, basically, the damping force is scarcely generated in therange of the small steering angles of the handlebar and it is increasedas the steering angle is lager. Furthermore, the damping coefficient ofthe cylindrical damper, i.e., the magnitude of the damping forcerelative to the amount of slidable displacement of the damper rod issmall in the range of the large steering angles; therefore, the dampingforce is prevented from being extremely increased even when thehandlebar is fully turned. Because of this, the rider is prevented fromfeeling hard steering during low-speed traveling which may require largesteering angles while characteristics required for the steering damperdevice for motorcycles or the like are maintained in which the dampingforce is increased according to the increased steering angle of thehandlebar.

According to another embodiment of the present invention, a steeringdamper device having a cylindrical damper is provided between a steeringside member turned around a steering stem by operating a handlebar and avehicle body side member not turned even by operating the handlebar. Thecylindrical damper includes a damper casing and a damper rod which isslidably displaced in the damper casing. As shown, for example, thesteering damper device is characterized in that a damping force appliedto the steering side member from the cylindrical damper is small when asteering angle of the handlebar is in the vicinity of 0° and the dampingforce is larger as the steering angle is progressively changed from 0°;and that a damping coefficient of the cylindrical damper is large whenthe steering angle of the handlebar is in the vicinity of 0° and thedamping coefficient is smaller when the steering angle is progressivelychanged from 0°.

Therefore, the rider is prevented from feeling hard steering duringlow-speed traveling which may require large steering angles whilecharacteristics required for the steering damper device for motorcyclesor the like is maintained in which the damping force is increasedaccording to the increased steering angle of the handlebar.

According to another embodiment of the present invention, a steeringdamper device having a cylindrical damper is provided between a steeringside member turned around a steering stem by operating a handlebar and avehicle body side member not turned even by operating the handlebar. Thecylindrical damper having a damper casing and a damper rod is slidablydisplaced in the damper casing. As shown, for example, the steeringdamper device is characterized in that an amount of slidabledisplacement of the damper rod with respect to a steering angle of thehandlebar is small when the steering angle of the handlebar is in thevicinity of 0° and the amount of slidable displacement is lager as thesteering angle is progressively changed from 0°; in that a damping forceapplied to the steering side member from the cylindrical damper is smallwhen a steering angle of the handlebar is in the vicinity of 0° and thedamping force is larger as the steering angle is progressively changedfrom 0°; and in that a damping coefficient of the cylindrical damper islarge when the steering angle of the handlebar is in the vicinity of 0°and the damping coefficient is smaller as the steering angle isprogressively changed from 0°.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will be described withreference to the accompanying drawings, wherein:

FIG. 1 is a side view of a front portion of a motorcycle equipped with asteering damper device according to a first embodiment of the presentinvention;

FIG. 2 is a front view of a front fork portion as viewed from thedirection of arrow 2 of FIG. 1;

FIG. 3 is a cross-sectional view of a cylindrical damper taken alongline 3-3 of FIG. 2;

FIG. 4 is an enlarged cross-sectional view taken along line 4-4 of FIG.3;

FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 4;

FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 4;

FIG. 7 is an exploded perspective view of the piston of the cylindricaldamper;

FIG. 8 is a front view, as with FIG. 2, showing a state where ahandlebar is turned from the neutral position to the left;

FIG. 9 is a cross-sectional view taken along line 9-9 of FIG. 8;

FIG. 10 is a characteristic curve diagram of the steering damper device;

FIG. 11 is a longitudinal sectional side view showing the cylindricaldamper of the steering damper device according to another embodiment ofthe present invention;

FIG. 12 is a longitudinal sectional side view showing the same as thatof FIG. 11 but the operating state thereof;

FIG. 13 is a cross-sectional view taken along line 13-13 in FIG. 11;

FIG. 14 is a cross-sectional view taken line 14-14 in FIG. 11;

FIG. 15 is a longitudinal sectional side view showing the cylindricaldamper of the steering damper device according to another embodiment ofthe present invention;

FIG. 16 is a longitudinal sectional side view showing the same as thatof FIG. 15 but the operating state thereof;

FIG. 17 is a cross-sectional view taken along line 17-17 in FIG. 15;

FIG. 18 is a cross-sectional view taken line 18-18 in FIG. 15;

FIG. 19 is a side view of a fork bridge portion of a front fork in amotorcycle equipped with the steering damper device according to anotherembodiment of the present invention; and

FIG. 20 is a front view as viewed from the direction of arrow 20 in FIG.19.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention will be described hereinafter withreference to the accompanying drawings. It is to be noted that thedrawings should be viewed in the direction of the reference characters.

FIGS. 1 to 10 illustrate a steering damper device according to a firstembodiment of the present invention.

As shown in FIGS. 1 and 2, a front fork 2 supporting a front wheel 1 ofa motorcycle includes right and left fork pipes 3, 3 and a fork bridge 4adapted to couple the upper end portions of the fork pipes 3, 3together. The fork bridge 4 is comprised of a top bridge 4 a and abottom bridge 4 b spaced vertically from and parallel to each other. Asteering stem 5 is provided to connect the top and bottom bridges 4 a, 4b at a horizontally central position therebetween. The steering stem 5is rotatably inserted into a head pipe 6 h provided at the front end ofa body frame 6. A handlebar 7 is attached to the top bridge 4 a forsteering. Thus, the motorcycle is steered by operating the handlebar 7to turn the front fork 2 clockwise and counterclockwise around thesteering stem 5, thereby turning the front wheel 1 supported by thefront fork together therewith.

The head pipe 6 h is provided with a stay 8 projecting forward at aposition closer to the lower end thereof. The stay 8 is located on thebody-central plane extending in the longitudinal direction of thevehicle body. The bottom bridge 4 b is provided with another stay 9projecting forward at the horizontally central position thereof. Thecylindrical damper 10 is mounted between both of the stays 8, 9. Inother words, the cylindrical damper 10 is disposed in front of the headpipe 6 h, extending substantially along the longitudinal directionthereof.

As shown in FIG. 3, the cylindrical damper 10 is composed of a dampercasing 11 and a damper rod 12 which is slidably displaced in the dampercasing 11. The damper casing 11 is rotatably connected through aspherical joint 13 to a side of the head pipe 6 h, i.e., to the stay 8on the body side. The damper rod 12 is rotatably connected through aspherical joint 14 to a side of the bottom bridge 4 b, i.e., to the stay9 on the steering side. The central axis of the damper rod 12 slidablydisplaced in the damper casing 11, i.e., the central axis D of thecylindrical damper 10 is designed to extend along each of the centralaxes of the spherical joints 13, 14. In this way, the cylindrical damper10 is mounted between the body frame 6 which is not turned even duringthe operation of the handlebar 7 and the front fork 2 which is turned bythe operation of the handlebar 7.

As shown in FIG. 2, the cylindrical damper 10 is in the most contractedstate when the handlebar 7 is in the neutral position, that is, when thesteering angle of the handlebar 7 is 0°. In addition to this, thecentral axis D of the cylindrical damper 10 is allowed to be parallel tothe central axis S of the steering stem 5. Thus, the central axis D ofthe cylindrical damper 10 is located on a plane in the longitudinaldirection of the body, including the central axis S of the steering stem5, that is, on the central plane of the body.

The damper casing 11 of the cylindrical damper 10 includes, as shown inFIG. 3, a damper chamber 15 and a reservoir 17 communicating with thedamper chamber 15 via an oil passage 16. The damper chamber 15 and thereservoir 17 are filled with oil. The bottom of the reservoir 17 isdefined by a piston 18. The piston 18 is upwardly biased under pressureby a compressed gas 19 filled in a gas chamber located thereunder. Thedamper chamber 15 is partitioned into two chambers, i.e., upper andlower chambers 15 a, 15 b, by a piston 20 attached to the top end of thedamper rod 12.

As shown in FIGS. 4 to 7, the piston 20 has a piston body 23 formed withpluralities of notches 21, 21, . . . ; 22, 22, . . . on the peripheriesof the upper and lower portions thereof, respectively. The piston body23 is provided with first through-holes 24, 24, . . . and secondthrough-holes 25, 25, . . . , which pass vertically therethrough. Thefirst through-holes 24 open at the respective upper ends into the upperend face of the piston body 23 and at the respective lower ends into thecorresponding notches 22, 22, . . . . The second through-holes 25 openat the respective lower ends into the lower end face of the piston body23 and at the respective upper ends into the corresponding notches 21,21, . . . . The upper ends of the first through-holes 24 arecontrollably opened and closed by a valve plate 26 made of an elasticplate; the lower ends of the second through-hole 25 are controllablyopened and closed by a similar valve plate 27. The upper valve plate 26is at its central portion secured through a washer 29 with a nut 28screwed onto the upper end of the damper rod 12. The upper valve plate26 is at its peripheral portion biased downwardly under pressure througha washer 31 with a valve spring 30 disposed compressively between theupper end face of the damper chamber 15 and the washer 31. Consequentlythe upper valve plate 26 is normally maintained in close contact withthe upper end face of the piston body 23. The washer 31 is also providedwith a plurality of notches 31 a, 31 a, . . . on the periphery thereof.A valve spring 33 is compressively disposed between the lower valveplate 27 and a valve receiver 32 carried by the damper rod 12. The lowervalve plate 27 is at its central portion biased under pressure upwardly.Consequently the lower valve plate 27 is maintained in close contactwith the lower end face of the piston body 23. The upper valve spring 30has a sufficiently greater spring force than the lower valve spring 33.

With this configuration, when the cylindrical chamber 10 equipped withthe piston 20 is extended, the piston 20 attached to the top end of thedamper rod 12 is slidably displaced toward the lower side of the damperchamber 15, so that pressure in the lower chamber 15 b of the damperchamber 15 is increased. This pressure is applied to the bottom side ofthe valve plate 26 through the first through-holes 24 from the notches22 on the periphery of the lower end of the piston body 23. Theperiphery of the valve plate 26 is pushed up against the bias force ofthe valve spring 30 as denoted by the chain double-dashed line in FIG.4. That is, it is separated from the upper end face of the piston body23. This allows the oil in the lower chamber 15 b to flow to the upperchamber 15 a as denoted by solid arrows in FIG. 4. Thus, the resistancecaused by the oil passing through the gap between the valve plate 26 andthe piston body 23 generates a damping force. In this case, a loadapplied to the valve plate 26 from the valve spring 30 will be larger asthe amount of deflection, i.e., amount of compression of the valvespring 30 is larger. When the cylindrical damper 10 is contracted, thegap between the valve plate 26 and the piston body 23 is small; the gapis larger as the damper 10 is more extended. Thus, the dampingcoefficient of the damper 10, i.e., the magnitude of the damping forcerelative to the amount of slidable displacement of the damper rod 12 islarge when the damper is contracted; it is smaller as the damper is moreextended.

On the other hand, when the cylindrical damper 10 is contracted, thepressure in the upper chamber 15 a of the damper chamber 15 isincreased. This downwardly deforms a peripheral portion of the lowervalve plate 27 against the biasing force of the valve spring 33 asdenoted by a chain double-dashed line in the right-lower portion of FIG.4. As a result, the valve plate 27 is separated from the lower end faceof the piston body 23, which allows the oil in the upper chamber 15 a toflow through the second through-hole 25 to the lower chamber 15 b, asdenoted by the dashed arrows of FIG. 4. In this case, a pressing forceis small which is applied to the peripheral portion of the valve plate27 by the valve spring 33; therefore, the valve plate 27 is easilydeformed. Any damping force will scarcely be generated at this time.

A description will then be made of the operation of the steering damperdevice configured as above.

As described earlier, when the handlebar 7 is in the neutral position,that is, when the steering angle of the handlebar is 0°, the cylindricaldamper 10 is in the most contracted, i.e., the shortest state. In thisstate, if the handlebar 7 is turned to the left for example, then thefront fork 2 will be leftward turned around the steering stem 5 which isrotatably inserted into the head pipe 6 h of the body frame 6. Thebottom bridge 4 b constitutes part of the fork bridge 4 of the frontfork 2 is turned in the same way. Thus, the spherical joint 14 whichcouples the stay 9 provided in the horizontally central portion of thebottom bridge 4 b to the damper rod 12 of the cylindrical damper 10 isoffset from the body central plane extending in the longitudinaldirection of the vehicle body. In contrast, the spherical joint 13 whichcouples the stay 8 provided on the head pipe 6 h to the damper casing 11of the cylindrical damper 10 is not turned even if the handlebar 7 isturned. In other words, the spherical joint 13 is at the originalposition, that is, on the body central plane extending in thelongitudinal direction of the vehicle body. As a result, the cylindricaldamper 10 is extended, that is, the damper rod 12 is slidably displaceddownwardly in the damper casing 11 in FIG. 3, which causes the dampingforce.

When the handlebar 7 is turned to the right, the cylindrical damper 10is extended in the same way, that is, the damper rod 12 is slidablydisplaced downwardly in FIG. 3, which causes the damping force. In thisway, the cylindrical damper 10 is configured such that even when thehandlebar 7 is turned to either side, namely, to the right or left fromthe position where the steering angle of the handlebar 7 is 0°, thedamper rod 12 is slidably displaced in the same direction in the dampercasing 11.

In addition, when the handlebar 7 is turned to the right or left, theamount of extension of the cylindrical damper 10 is the same if the cutangle, namely the steering angle of the handlebar 7 is the same. Thus,the damping force characteristics are symmetrical to each other as shownin FIG. 10.

When the handlebar 7 which has been turned to the right or left isreturned to the neutral position, the cylindrical damper 10 iscontracted in either case, that is, the damper rod 12 is slidablydisplaced within the damper casing 11 upwardly in FIG. 3. As describedabove, the cylindrical damper 10 is designed to scarcely generate thedamping force. Therefore, the damping force is scarcely generated whenthe handlebar which has been turned is returned. In this way, thesteering damper device can generate the damping force in either case,that is, when the handlebar 7 is turned to the right or left from thesteering angle 0°. In addition, it can make the damping force smallerwhen the handlebar 7 is returned to the steering angle 0°.

With this steering damper device, the amount of extension of thecylindrical damper 10 relative to the steering angle of the handlebar 7is small when the handlebar 7 is in the vicinity of the neutralposition; in the range of the larger steering angle of the handlebar 7,the damper stroke is gradually increased according to the steering angleof the handlebar 7. More specifically, the amount of slidabledisplacement of the damper rod 12 relative to the steering angle of thehandlebar is small in the vicinity of 0° of the steering angle of thehandlebar. In addition, it is increased as the steering angle of thehandlebar is progressively changed from 0°. Thus, when the handlebar 7is turned from the neutral position, damping moment is scarcelygenerated at its early stage, and gradually increased in the middlestage, as shown in FIG. 10. To be more specific, the damping forceapplied from the cylindrical damper 10 to the front fork 2 as thesteering side member is small in the vicinity of 0° of the handlebarsteering angle and it is increased according as the handlebar steeringangle is progressively changed from 0°. The damping force continuessmoothly from the early stage to the middle stage. In this way, thissteering damper device can provide the characteristics desirable andpreferable for steering damper devices for motorcycles.

As described earlier, the damping coefficient of the cylindrical damper10, i.e., the magnitude of the damping force relative to the amount ofslidable displacement of the damper rod 12 is large when the damper 10is contracted; it is smaller as the damper 10 is more extended. Morespecifically, the damping coefficient is large when the handlebarsteering angle is in the vicinity of 0°; it is smaller as the handlebarsteering angle is progressively changed from 0°. Accordingly, in therange of the increased handlebar steering angles, while the amount ofthe slidable displacement of the damper rod 12 relative to the steeringangle of the handlebar is increased, the damping force is not increasedso much. As a result, the increase in damping moment is small in therange of the increased steering angle of the handlebar; therefore, thehandlebar can be operated nimbly even if it is turned fully to eitherside during the motorcycle is traveling at low speeds.

FIGS. 11 to 14 illustrate a steering damper device according to anotherembodiment of the present invention.

Incidentally, this embodiment is the same as the first embodiment interms of the overall configuration but with a cylindrical damperadopted. Components corresponding to those in the first embodiment aretherefore denoted by the same reference numerals and the duplicateexplanation will be omitted.

A cylindrical damper 40 of this embodiment is provided with a groove 41on the circumferential wall of a damper chamber 15 in place of the valvespring 30 of the cylindrical damper 10 in the first embodiment.

More specifically, also in the cylindrical damper 40 in this embodiment,the piston body 23 of a piston 20 is attached to the top end of a damperrod 12 and is formed with pluralities of notches 21, 21, . . . ; 22, 22,. . . on the peripheries of the upper and lower portions thereof,respectively. The piston body 23 is provided with first through-holes24, 24, . . . and second through-holes 25, 25, . . . , which passvertically therethrough. The first through-holes 24 open at therespective upper ends into the upper end face of the piston body 23 andat the respective lower ends into the corresponding notches 22. Thesecond through-holes 25 open at the respective lower ends into the lowerend face of the piston body 23 and at the respective upper ends into thecorresponding notches 21. The upper ends of the first through-holes 24are controllably opened and closed by a valve plate 26 made of anelastic plate; the lower ends of the second through-holes 25 arecontrollably opened and closed by a similar valve plate 27. The uppervalve plate 26 has relatively high-rigidity and is at its centralportion secured through a washer 29 with a nut 28 screwed onto the upperend of the damper rod 12. The upper valve plate 26 is normally retainedin close contact with the upper end face of the piston body 23. Thelower valve plate 27 is at its central portion biased under pressureupwardly by a valve spring 33 compressively disposed between the valveplate 27 and a spring receiver 32 carried on the damper rod 12.Consequently the lower valve plate 27 is maintained in close contactwith the lower end face of the piston body 23. The valve spring 33 has asmall spring force.

The damper chamber 15 is formed with the groove 41 on thecircumferential wall at a location which faces the piston body 23 whenthe cylindrical damper 40 is extended. The groove 41 extends verticallygreater than the vertical dimension of the piston body 23.

With the steering damper device provided with the cylindrical damper 40having such a configuration, when a handlebar 7 is in the neutralposition and the cylindrical damper 40 is most contracted, as shown inFIG. 11 the outer circumference of the piston body 23 is in entirecontact with the inner circumference of the damper chamber 15. When thehandlebar 7 is turned to the right or left from this state, the damper40 is extended, that is, the piston 20 attached to the top end of thedamper rod 12 is slidably displaced toward the lower portion of thedamper chamber 15. This increases the pressure in the lower chamber 15 bof the damper chamber 15. The pressure is applied from the notches 22 onthe outer periphery of the lower end of the piston body 23 through thefirst through-holes 24 to the bottom side of the valve plate 26. As aresult, the outer peripheral portion of the valve plate 26 is pushed upas denoted by double-dashed lines in FIG. 11, that is, separated fromthe upper end face of the piston body 23. The oil in the lower chamber15 b is allowed to flow to the upper chamber 15 a as denoted by solidarrows in FIG. 11. Thus, resistance caused by the oil passing throughthe gap between the valve plate 26 and the piston body 23 generates adamping force. In this case, since the valve plate 26 has high-rigidityand is relatively less deformable, the gap defined between the valveplate 26 and the piston body 23 at that time is small. Accordingly, thedamping coefficient of the damper 40 is large at that time.

When the damper 40 is extended to some extent and the piston body 23reaches a location facing the groove 41 as shown in FIG. 12, the oil inthe lower chamber 15 b of the damper chamber 15 is allowed to flow tothe upper chamber 15 a through the groove 41 as denoted by solid arrowsin FIG. 12. Consequently, resistance to the flowing oil becomes small.In other words, the damping coefficient of the damper 40 becomes small.

In this way, with also the damper 40, its damping coefficient, namely,the magnitude of damping force with respect to the amount of slidabledisplacement of the damper rod 12 is large when the damper 40 iscontracted; it is smaller as the damper 40 is more extended.

On the other hand, the pressure in the upper chamber 15 a of the damperchamber 15 is decreased when the damper 40 is contracted; therefore, thelower valve plate 27 is downwardly deformed at its peripheral portionagainst the biasing force of the valve spring 33 as denoted by thedouble-dashed chain line in the lower-right side in FIGS. 11 and 12. Asa result, a gap is defined between the valve plate 27 and the lower endof the piston body 23, so that the oil in the upper chamber 15 a isallowed to flow to the lower chamber 15 b through the secondthrough-holes 25 as denoted by dashed arrows in FIGS. 11 and 12. In thiscase, since the valve plate 27 is easily deformed, a damping force isscarcely generated at that time.

Thus, the steering damper device of this embodiment can provides thesame function and effect as that of the first embodiment.

FIGS. 15 to 18 illustrate a steering damper device according to anotherembodiment of the present invention. FIG. 15 is a longitudinal sectionalside view of the cylindrical damper of the steering damper device. FIG.16 is a longitudinal sectional side view showing the same as that ofFIG. 15 but the operating state thereof. FIG. 17 is a cross-sectionalview taken along line 17-17 in FIG. 15. FIG. 18 is a cross-sectionalview taken line 18-18 in FIG. 15.

Incidentally, this embodiment is the same as the first embodiment interms of the overall configuration but a cylindrical damper adopted.Components corresponding to those in the first embodiment are thereforedenoted by the same reference numerals and the duplicate explanationwill be omitted.

In place of the valve spring 30 in the cylindrical damper 10 of thefirst embodiment, a cylindrical damper 50 of this embodiment is providedwith a passage 51 at the top end of a damper rod 12. A variablenarrowing mechanism is provided in the passage 51.

In the damper 50 of this embodiment, a piston 20 attached to the top endof the damper rod 12 has the same configuration as that of thisembodiment. At the top end of the damper rod 12, the passage 51 isprovided which is made up of a central hole 51 a and radial holes 51 b.The central hole 51 a opens in the upper chamber 15 a of a damperchamber 15 at the upper end face of the damper rod 12 and terminates ata position lower than the mounting portion of the piston 20. The radialholes 51 b are adapted to establish communication between the centralhole 15 a and the lower chamber 15 b of the damper chamber 15. On theother hand, the damper chamber 15 is at its upper end face formed with atapered projection 52, which protrudes from the center of the upper endface downwardly and is reduced in diameter progressively downwardly. Theprojection 52 is inserted into the central hole 51 a at the top end ofthe damper rod 12.

With the steering damper device provided with the cylindrical damper 50having such a configuration, when the handlebar 7 is in the neutralposition and the damper 50 is most contracted, the upper end of thecentral hole 51 a of the damper rod 12 faces the diameter-increasedportion of the projection 52. The gap defined therebetween is,therefore, small, that is, the area of the passage 51 is small. When thehandlebar 7 is turned to the right or left from this state, the damper50 is extended, that is, the piston 20 attached to the top end of thedamper rod 12 is slidably displaced toward the lower side of the damperchamber 15. The pressure in the lower chamber 15 b of the damper chamber15 is therefore increased. This allows the oil in the lower chamber 15 bto pass through the passage 51 formed in the damper rod 12 as denoted bysolid arrows in FIG. 15. At the same time, as with this embodiment, thisallows the oil to flow from the first through-holes 24 through the gapbetween the valve plate 26 and the piston body 23 to the upper chamber15 a. Resistance applied to the oil at this time generates a dampingforce. In this case, an area defined in the passage 51 is small, and asdescribed above, also the gap defined between the valve plate 26 and thepiston body 23 is small. Thus, the damping coefficient of the damper 50is large.

When the damper 50 is extended according to the steering angle of thehandlebar 7, the upper end of the central hole 51 a of the damper rod 12will face the diameter-reduced portion of the projection 52. The area ofthe passage 51 is therefore increased, so that resistance to the flow ofthe oil is decreased. In other words, the damping coefficient of thedamper 50 is decreased.

In this way, with the cylindrical damper 50, its damping coefficient,namely, the magnitude of the damping force with respect to the amount ofslidable displacement of the damper rod 12 is large when the damper 50is contracted; it is smaller as the damper 50 is more extended.

On the other hand, when the damper 50 is contracted, the pressure in theupper chamber 15 a of the damper chamber 15 is increased. As with thisembodiment, the oil in the upper chamber 15 a is therefore allowed toflow through the second through-holes 25 to the lower chamber 15 b asshown in the dashed arrows of FIGS. 15 and 16. In this case, since thevalve plate 27 is easily deformed, the damping force is scarcelygenerated at this time.

Thus, the steering damper device of this embodiment can provide the samefunction and effect as those of the first embodiment.

FIGS. 19 and 20 illustrate a steering damper device according to anotherembodiment of the present invention.

In this embodiment, components corresponding to those in the firstembodiment are denoted by the same reference numerals and the duplicateexplanation will be omitted.

In this embodiment, as shown in FIGS. 19 and 20, a substantiallytriangular link lever 58 is rotatably carried by the front end of a stay8 a through a horizontal shaft 59. The stay 8 a projects forwardly fromthe vertically central portion of a head pipe 6 h. A cylindrical damper60 is disposed between the link lever 58 and the upper end of the headpipe 6 h. The damper 60 is composed of a damper casing 61 and a damperrod 62 slidably displaced within the damper casing 61. The damper casing61 is rotatably connected to the front of the upper end of the head pipe6 h through a horizontal shaft 63. The damper rod 62 is rotatablyconnected to the front end of the link lever 58 through a horizontalshaft 64. On the other hand, a link rod 65 is rotatably connected to thefront of the lower end of the link lever 58 through a spherical joint66. The other end of the link rod 65 is rotatably connected through aspherical joint 67 to the front of the horizontal central portion of abottom bridge 4 b, which is a lower part of the fork bridge 4.

In this way, the cylindrical damper 60 is connected to a body frame 6which is not turned even by operating a handlebar, while connectedthrough the link lever 58 and the link rod 65 to the fork bridge 4 as asteering side member which is turned around a steering stem 5 byoperating the handlebar. The link rod 65 is disposed in the followingmanner. When the handlebar 7 is in the neutral position, that is, thesteering angle of the handlebar is 0°, a straight line L connecting therespective centers of the spherical joints 66, 67 is located on thecentral plane extending along the longitudinal direction of the vehiclebody and including the central axis S of the steering stem 5. Thespherical joints 66, 67 serve respectively as connecting parts atopposite ends of the link rod 65.

The cylindrical damper 60 has the same configuration as those of theaforementioned cylindrical dampers 10, 40, 50. When it is extended, adamping force is generated. In contrast, when it is contracted, thedamping force is scarcely generated. In addition, its dampingcoefficient is large when the steering angle of the handlebar is in thevicinity of 0°; it is smaller as the steering angle is progressivelychanged from 0°.

The other configurations of this embodiment are the same as those of thefirst embodiment.

With the steering damper device configured as described above, when thehandlebar 7 is turned to the left for example, then the front fork 2 isturned to the left with respect to the central axis S of the steeringstem 5, whereby the bottom bridge 4 b is turned in the same way. Thespherical joint 67 coupled to the front center of the bottom bridge 4 bis displaced to a position denoted by the double-dashed chain line inFIG. 20. As a result, the spherical joint 66 coupled to the link lever58 is pulled down by the link rod 65 coupled to the spherical joint 67,and in turn, the link lever 58 is turned around the horizontal shaft 59as denoted by the arrow in FIG. 19. Thus, the damper 60 is extended toapply a damping force to the bottom bridge 4 b as the steering sidemember. Likewise, when the handlebar 7 is turned to the right, thespherical joint 66 on the side of the link lever 58 is pulled down, sothat the damper is extended in the same way, generating the dampingforce.

If the handlebar 7 is fully turned, while the amount of extension of thedamper 60 is large, the damping coefficient is designed to be small atthat time. This makes the damping force generated not large so much.Thus, this also prevents the rider from feeling hard steering.

When the handlebar which has been turned to the right or left isreturned to the neutral position, the damper 60 is contracted in eithercase, so that a damping force is scarcely generated.

In this way, the steering damper device of this embodiment can providethe same effect as that of the first embodiment. For this steeringdamper device, the movement of the steering side members is transmittedto the cylindrical damper 60 through the link rod 65 and the link lever58; therefore, the damper 60 can be disposed so as to be disengaged fromthe steering side members and placed in any direction. Thus, the damper60 can be arranged in a further free manner.

While the preferred embodiments of the present invention have beendescribed so far, the invention shall not be limited to the embodimentsand various modifications can be made without departing from the scopeof the invention.

For example, the cylindrical damper 10 may be of a double-tube type inwhich a reservoir is provided on the outer circumference of the damperchamber in addition to a type in which the reservoir 17 is provided onthe side of the damper chamber 15 as with each embodiment describedabove. A compression spring may be used in place of the compressed gas19 for biasing the piston 18 provided on the side of the reservoir 17,and both may be provided. Further, the present invention is applicableto four-wheel buggies and other vehicles in addition to theabove-mentioned motorcycles.

In addition, a cylindrical damper may be applicable in which it is thelongest when the steering angle of a handlebar is near 0° and it can bedisposed in the longitudinal direction of a vehicle body. In such acase, the damper is not necessarily disposed in such a manner as to belocated on the central plane in the longitudinal direction of thevehicle body when the handlebar 7 is on the neutral position. The dampercan be disposed in such a manner as to be slightly offset from thecentral plane in the longitudinal direction of the vehicle body.Further, the cylindrical damper 10 can be disposed between the bodyframe 6 and the top bridge 4 a of the fork bridge 4 or the like.

1. A steering damper device having a cylindrical damper provided betweena steering side member and a vehicle body side member, said cylindricaldamper comprising: a damper casing and a damper rod which is slidablydisplaced in said damper casing, wherein an amount of slidabledisplacement of the damper rod with respect to a steering angle of thehandlebar is small when the steering angle of the handlebar is near 0°and the amount of slidable displacement is larger as the steering angleis progressively changed from 0°; and a damping coefficient of thecylindrical damper is large when the steering angle of the handlebar isnear 0° and the damping coefficient is smaller when the steering angleis progressively changed from 0°.
 2. A steering damper device having acylindrical damper provided between a steering side member and a vehiclebody side member, said cylindrical damper comprising: a damper casingand a damper rod which is slidably displaced in said damper casing,wherein a damping force applied to the steering side member from thecylindrical damper is small when a steering angle of the handlebar isnear 0° and the damping force is larger as the steering angle isprogressively changed from 0°; and a damping coefficient of thecylindrical damper is large when the steering angle of the handlebar isin the vicinity of 0° and the damping coefficient is smaller when thesteering angle is progressively changed from than 0°.
 3. A steeringdamper device having a cylindrical damper provided between a steeringside member and a vehicle body side member, said cylindrical dampercomprising: a damper casing and a damper rod which is slidably displacedin said damper casing, wherein an amount of slidable displacement of thedamper rod with respect to a steering angle of the handlebar is smallwhen the steering angle of the handlebar is near 0° and the amount ofslidable displacement is lager as the steering angle is progressivelychanged from 0°; a damping force applied to the steering side memberfrom the cylindrical damper is small when a steering angle of thehandlebar is in the vicinity of 0° and the damping force is larger asthe steering angle is progressively changed from 0°; and a dampingcoefficient of the cylindrical damper is large when the steering angleof the handlebar is in the vicinity of 0° and the damping coefficient issmaller as the steering angle is progressively changed from 0°.